"bus which carries passengers for a fare," 1915, short for jitney bus (1906), American English, from gitney, said to be slang for any small coin, especially "a nickel," because the buses' fare typically was a nickel, the coin name perhaps via New Orleans from French jeton "coin-sized metal disk, slug, counter," from Old French jeter "to calculate," literally "to throw" (see jet (v.)).

"I'll give a nickel for a kiss,"
Said Cholly to a pretty miss.
"Skiddo," she cried, "you stingy cuss,"
"You're looking for a jitney buss."

["Jitney Jingle," 1915]

The origin and signification of the word was much discussed when the buses first appeared. Some reports say the slang word for "nickel" comes from the bus; most say the reverse, but there does not seem to be much record of jitney in a coin sense before the buses came along (a writer in "The Hub," August 1915, claims to have heard and used it as a small boy in San Francisco, and reported hearsay that "It has been in use there since the days of '49." In some sources it is said to be a St. Louis word, but most credit it to the U.S. West, especially California, though others trace it to "southern negroes, especially in Memphis" ["The Pacific," Feb. 7, 1915].